Page 2 of 4 FirstFirst 1234 LastLast
Results 14 to 26 of 47
  1. #14
    Join Date
    Dec 2006
    Location
    Arkansas
    Posts
    292
    I have had great success with the correct size without having to add the extra capacity. The answer to "undersized" units may not be a larger one, because it may be lacking the capacity because of duct problems or other reasons. I don't ever remember seeing a calculation done right and an installation done right to match the calculation being a problem. One of the two have to be wrong, or a combination of minor problems with both.

    I was not really addressing a professional that knows what they are doing such as you and TB installing what is right for a specific situation. My point was for the casual person surfing this board that sees a pro recommend extra capacity, then takes that to someone that does not do things right and asks for the extra capacity on top of a system that is probably already too large.

    I think we have all seen disgusting jobs (too small, too large, poor design, poor installation, etc.) done by other "professionals" and it makes it hard when we say "call a pro" yet the person asking has been already burned by a "pro". But I hope anyone that reads a few of these posts will be able to learn enough to sort out the good from the bad.

  2. #15
    Join Date
    Nov 2007
    Location
    Sherman, TX
    Posts
    9,441

    To Clarify

    The particular contractor that I followed so many times, was notorious for using larger indoor coils to gain higher SEER "rating" as opposed to providing the actual desired SEER equipment.

    For example, they would install a 9 SEER 3 ton condenser, with a 9 SEER 4 ton coil, and call it 3 ton 11 SEER.

    A half ton oversized coil is no biggie, in my book, but I see some really radical stuff. I have an elderly customer who has a five ton cap tube slab coil with a 3 1/2 ton condensing unit. She's convinced that it works fine, and since she's on a "fixed income" I can't convince her to replace either component.

  3. #16
    Join Date
    Dec 2006
    Location
    Arkansas
    Posts
    292
    Those are a couple of good examples to store away in my "really dumb" file. I would agree that the 1/2 ton is not a big deal. I wish we could educate homeowners to understand that those types of situations are to be avoided and to find someone that knows what they are doing, but there will always be someone that will give in, mostly because of the price.

  4. #17
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,646
    I was hoping for more discussion about the lack of latent capacity at the lower/no sensible cooling loads. Maintaining <50%RH during cool wet weather with dehumidification, eliminates the critical a/c sizing issue. An extra .5 ton of cooling capacity is great as equipment ages or the equipment is not available in .5 ton sizes. The most negative issue with large cooling coils is the 2 lbs. per ton of moisture retained on the coil between cycles. A 4 ton has 6-8 lbs. of retained water that slowly evaporates into the ducts keeping the ducts wet for days. One lb. of water evaporating raises the %RH in 1,000 sqft. of home 8%RH. Supplemental dehumidification allows for daily drying of the ducts to prevent mold growth over the long term. IAQ requires maintaining <50%RH throughout the home and the air handling systems to avoid mold growth. Low humidity is also a comfort issue. Regards TB
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  5. #18
    Join Date
    Oct 2007
    Location
    STL Metro East
    Posts
    20
    That is exactly why I was asking about the negatives that come with an oversized coil. But, when the alternative is to go to a 4 ton heat pump with the same 4 ton coil, wouldn't you end up with the same amount of moisture in the coil along with longer periods without air movement?

  6. #19
    Join Date
    Jul 2006
    Location
    Virginia
    Posts
    238
    Quote Originally Posted by teddy bear View Post
    The most negative issue with large cooling coils is the 2 lbs. per ton of moisture retained on the coil between cycles. A 4 ton has 6-8 lbs. of retained water that slowly evaporates into the ducts keeping the ducts wet for days. One lb. of water evaporating raises the &#37;RH in 1,000 sqft. of home 8%RH. Supplemental dehumidification allows for daily drying of the ducts to prevent mold growth over the long term. IAQ requires maintaining <50%RH throughout the home and the air handling systems to avoid mold growth. Low humidity is also a comfort issue. Regards TB
    A four ton unit holds almost a gallon in its coil! I had no Idea they held that much water. I knew my coil had a lot of water when I ran the fan continously during low demand cooling days. I swear I could feel the humidity actually rise.

    Also I am supprised no one has suggested a dual stage unit. My heat load calc came out on the edge of three ton or 2.5 ton so I went with a dual stage unit. two ton low, three high. Unfortunantly/fortunantly my ground loop is so efficient due to the saturated soil I am actually running in the four ton range on high.

  7. #20
    Join Date
    Dec 2006
    Location
    Arkansas
    Posts
    292
    Quote Originally Posted by teddy bear View Post
    I was hoping for more discussion about the lack of latent capacity at the lower/no sensible cooling loads. Maintaining <50%RH during cool wet weather with dehumidification, eliminates the critical a/c sizing issue. An extra .5 ton of cooling capacity is great as equipment ages or the equipment is not available in .5 ton sizes. The most negative issue with large cooling coils is the 2 lbs. per ton of moisture retained on the coil between cycles. A 4 ton has 6-8 lbs. of retained water that slowly evaporates into the ducts keeping the ducts wet for days. One lb. of water evaporating raises the %RH in 1,000 sqft. of home 8%RH. Supplemental dehumidification allows for daily drying of the ducts to prevent mold growth over the long term. IAQ requires maintaining <50%RH throughout the home and the air handling systems to avoid mold growth. Low humidity is also a comfort issue. Regards TB
    TB - Why would you need the extra .5 ton if you used a dehumidifier? If you don't need to remove the sensible heat, wouldn't the dehumidifier maintain the humidity?

  8. #21
    Join Date
    Oct 2005
    Location
    MN
    Posts
    133
    What are the drawbacks (During Heating)of oversizing the coil on a heat pump system?

  9. #22
    Join Date
    Apr 2005
    Location
    Kingston Ontario Canada
    Posts
    1,234
    Quote Originally Posted by teddy bear View Post
    I was hoping for more discussion about the lack of latent capacity at the lower/no sensible cooling loads. Maintaining <50%RH during cool wet weather with dehumidification, eliminates the critical a/c sizing issue. An extra .5 ton of cooling capacity is great as equipment ages or the equipment is not available in .5 ton sizes. The most negative issue with large cooling coils is the 2 lbs. per ton of moisture retained on the coil between cycles. A 4 ton has 6-8 lbs. of retained water that slowly evaporates into the ducts keeping the ducts wet for days. One lb. of water evaporating raises the %RH in 1,000 sqft. of home 8%RH. Supplemental dehumidification allows for daily drying of the ducts to prevent mold growth over the long term. IAQ requires maintaining <50%RH throughout the home and the air handling systems to avoid mold growth. Low humidity is also a comfort issue. Regards TB
    Hi Teady Bear: In your sig line you indicate use a +10 merv filter. I have been led to believe that high merv filters are too restrictive. Would you be so kind to elaborate on this subject for me?

    Thanks

    thorton
    ____________________
    You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals

  10. #23
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,646
    Quote Originally Posted by dcmcm5 View Post
    TB - Why would you need the extra .5 ton if you used a dehumidifier? If you don't need to remove the sensible heat, wouldn't the dehumidifier maintain the humidity?
    Need? Yes, a properly set-up simple a/c will maintain <50%RH during the higher cooling loads without operating the dehu. Size the a/c as small as you feel comfortable with. It is ok with me if you willing to live with a little extra temperature during the extremes.
    In the past, not being over-sized has been said to be the key to being able to maintain low humidity during low/no cooling conditions. Manual J is an estimate based on measurements and needs.
    True, being grossly over-sized increases short cycling. As the load decreases, The cycles increase and the latent also declines. This happens with under-sized system also. The down side of be too closely sized, is to not have the extra capacity for rapid cool down needed for t-stat set-up when the home routinely unoccupied. Extra capacity for maintaining comfort with having extra occupants during extreme hot weather. Over the life of the a/c system, the capacity of a compressor declines with age. Aging homes may also lose insultation value and require a more cooling capacity. All of these things indicate a distinct advantage of having a little extra initial cooling capacity. It has nothing to do with having a dehumidifier. The dehu means being able to maintain <50% RH independent of the cooling load or weather conditions. Turn off the a/c when unoccupied without fear of moisture damage, odors, or mold growth. This allows for a significant reduction in energy consumption. I routinely hear from people who set-up there t-stat to 80^F with maintaining 45%RH. With a little extra capacity, lowering the t-stat for individual comfort is doable. All of these points are big advantages compared to over-cooling two speed compressors with over-sized cooling coils to try to provide comfort. Regards TB
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  11. #24
    Join Date
    Jun 2004
    Location
    4H: Hot, Humid Houston H.O.
    Posts
    3,304
    It might be very interesting as Teddy Bear says, to discuss the latent capacity at low AC duty cycle, i.e. mild temperatures. Sure wish it were easy to measure condensate removed, then we could talk empirically, and learn more about AC systems which do and don't remove humidity effectively to needs. But near as I can tell the mechanism to do so is either labor intensive (a calibrated container) or expensive, so we seem doomed to talk theory.

    The point I am wondering about is, just how much does this worst-case weather pattern for humidity occur, that TB talks about as an example. In my S.Texas region, there is a narrow temperature range where it applies, and we don't spend much time with rain in that range. Below about 65F and the temperature will tend to help the house out in terms of outdoor dewpoint. Above about 75F and we do want to run the air conditioner, and the concept of overcooling seems debatable.

    Of course I don't want to talk only about my region, but any and all. I'm still trying to get my mind wrapped around the principles that apply here.

    Best wishes -- Pstu

  12. #25
    Join Date
    Oct 2007
    Location
    STL Metro East
    Posts
    20
    Teddy Bear, your company needs to hook up with the heating and cooling companies to package a total solution. I would pay extra to get the full heating/cooling/humidification/dehumidification treatment for my house without patching together multiple strategies. In fact, I have been waiting for this capability since the first computer room solution that I saw perform these functions in the early 80's. Until these all come together, it sure would help me if the companies would give us back our choices of size instead of relying on the multi-stage heating and cooling to cut their inventory.

  13. #26
    Join Date
    Jun 2007
    Location
    Metro St. Louis
    Posts
    181
    Quote Originally Posted by teeoff View Post
    I am actually in Illinois, just across the river from Arnold. I did not plan to get this involved in sizing the equipment, but the only contractor who offered to do an actual load calculation has not called back for 2 weeks. I was just using 72%, just trying to get in the ballpark. As you can see, we are right on the edge with a 3 ton heat pump & with the Carrrier Infinity we were looking at, the next step up is 4 tons. Since we were looking for a dual fuel system, that also required a jump to an 80,000 BTU furnace instead of the 60,000 to get enough airflow capacity. Our house is built with insulated concrete forms which also complicates the calculations, the extra mass in the walls has a smoothing effect on the thermal load. Our AC may not run as much during the hottest part of the day, but the heat does not disappear when the sun goes down, so our AC runs more at night than our neighbors'. We also don't do the setbacks because my wife teaches piono in the house, so there is always someone home.
    Hello Columbia. Used to live on Ferkel Street a few years ago.

    I recently had a heat pump put in. Original homeowner didn't want gas, so we had an electric furnace. Winter bills were beyond painful. Had two months each of the last two winters with over 4000 KWH used.

    Talked to around 10 contractors, since I was thinking about either gas or geothermal. Quite a range of folks - from one-man shops to big outfits. If you would like addtl info on the contractors I had visit and my perceptions of them, send me an email (see my profile).

    One concern - stepping up from 3 tons to 4 tons may increase the noise in your ductwork. Probably not good for piano lessons.

    Best of luck...

Page 2 of 4 FirstFirst 1234 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event